In recent years, methods for stereolithography using liquid photocuring resin compositions based on data inputted with three-dimensional CAD have been widely employed because intended 3-dimensional article can be produced in good dimensional accuracy without fabricating a die assembly and the like.
A typical example of stereolithography may include a method in which ultraviolet laser controlled by a computer so as to obtain a desired pattern is selectively radiated to a liquid surface of a liquid photocuring resin placed in a container to cure through a predetermined thickness, followed by supplying the liquid resin for one layer onto the cured layer and radiating ultraviolet laser for curing similarly as above, and thus laminating operation for obtaining subsequent cured layers is repeated, and thereby a 3-dimensional article is finally obtained. Such method of stereolithography enables to easily obtain a 3-dimensional article even in a fairly complex form for a relatively short time period.
Still in recent years, instead of the conventional methods described above using spot ultraviolet laser light, stereolithography techniques have been proposed that sequentially form photocured resin layers having a predetermined sectional form pattern by radiating light to a liquid surface of a photocuring resin through a liquid crystal paint mask having a large number of liquid crystal microshutters capable of shading and transmitting light in microdot area and disposed in a sheet-like form, or a sheet-like print mask made of so-called DMD (digital micromirror device) having a plurality of digital micromirror shutters disposed in a sheet-like form between a light source and a surface of a photocuring resin composition. Since the stereolithography techniques using a print mask can radiate light to a fabrication surface made of a photocuring resin composition in a sheet-like form at one time to form a photocured sectional form pattern in a sheet-like form at one time, they can remarkably improve the stereolithography speed compared with a stippling system using spot ultraviolet laser.
Various properties are required for resin compositions used for stereolithography, such as good handling property during fabrication due to low viscosity, stable physical and curing properties due to less absorption of water and moisture over time before curing the resin compositions, high curing sensitivity for active energy rays, good curing properties in an oxygen atmosphere, excellent fabrication accuracy with high resolution of 3-dimensional article thereof, a low volume shrinkage after curing, excellent mechanical properties of cured products thereof, and excellent dimensional stability for less water and moisture absorption over time due to excellent water resistance and moisture resistance of cured products thereof.
As a resin composition for stereolithography, acrylate photocuring resin compositions, urethane acrylate photocuring resin compositions, epoxy photocuring resin compositions, epoxy acrylate photocuring resin compositions, and vinyl ether photocuring resin compositions have been conventionally proposed and employed. Among these, epoxy photocuring resin compositions in particular have attracted attention recently because of the good dimensional accuracy of fabricated products obtained therefrom.
Such epoxy photocuring resin compositions, however, are pointed out that the reaction speed is slow because reaction proceeds with cations generated by light irradiation, and thus fabrication takes too much time. Under such circumstances, to increase the reaction speed, such epoxy photocuring resin compositions are proposed to be added with low molecular weight polyol compounds, such as ethylene glycol and propylene glycol. Moreover, for the purpose of reduction in fabrication time by improving the reaction speed, a resin composition for stereolithography is proposed in which a polyester polyol compound is added to a photocuring resin composition including a cationically polymerizable organic compound, such as epoxy compounds, and a radical polymerizable organic compound (Patent Document 1). In either case however, since the curing speed during photocuring is slow, stereolithography takes time and fabricated products thus obtained are not cured sufficiently and does not have sufficient mechanical properties. Furthermore, fabricated products thus obtained have low dimensional accuracy, and also have problems in water resistance and moisture resistance.
With these points in mind, the present inventors kept on conducting researches with an object to provide a resin composition for stereolithography which has high curing sensitivity for active energy rays to be able to produce a 3-dimensional article productively for reduced active energy ray irradiation time; which is excellent in resolution and fabrication accuracy to be able to produce a fabricated product with intended dimensions; a cured product of which has a low volume shrinkage after curing thus having high dimensional accuracy and has excellent water resistance and moisture resistance, absorbing less water and moisture over time, and is excellent in dimensional stability, and still further excellent in mechanical properties. Then, they found that, in a case where oxetane monoalcohol expressed by the general formula (II) below;
(wherein R3 denotes an alkyl group, an aryl group, or an aralkyl group, and n denotes an integer from 1 to 6) is contained in a resin composition for stereolithography, when fabricated using a resin composition for stereolithography obtained thereby, a 3-dimensional article that is excellent in water resistance and moisture resistance, and moreover, is excellent in dimensional accuracy, dimensional stability, and mechanical properties can be productively produced at high reaction speed and high fabricating speed for reduced active energy ray irradiation time, and applied for patent in advance (Patent Document 2).
The present inventors have further continued studies regarding the resin composition for stereolithography of Patent Document 2 and the physical properties of a 3-dimensional article obtained therefrom. As a result, it was found that, to produce a 3-dimensional article for shorter time by smoothly controlling the fabrication time, the water and moisture absorption over time before curing the resin composition for stereolithography has to be further less.    [Patent Document 1] Japanese Examined Patent Publication No. H07-103218    [Patent Document 2] Japanese Unexamined Patent Publication No. H11-199647    [Non-Patent Document 1] Paul F. Jacobs, “Rapid Prototyping & Manufacturing, Fundamentals of Stereo-Lithography”, “Society of Manufacturing Engineers”, 1992, p. 28-39.